February 2016

Dynamic warm-up with balance, plyo work leads to safer landings

Helps protect ACL in both genders

By Chris Klingenberg

A one-time neuromuscular training intervention designed to prevent anterior cruciate ligament (ACL) injury is more effective than a traditional warm-up for improving landing technique in youth athletes, according to a study that could help convince coaches and athletes to embrace such training programs.

“While there is existing evidence in studies that have followed athletes across a whole season and seen improvements, we feel that the strength of our findings is that they can be used as support for initial buy-in from coaches and athletes,” said Hayley Root, MS, ATC, a doctoral student in the Human Performance Lab at the University of Connecticut in Storrs and first author of the study. “It would be difficult to extrapolate our specific findings, as there is such a strong link between program compliance, exercise fidelity, and dosage with end-of-season results.”

In the study, 89 active children (29 girls; age = 13 ± 2 years, height = 161.57 ± 12.57 cm, mass = 56.14 ± 13.46 kg) were randomized into one of three warm-up groups. The participants were in grades five through nine and were members of a fall or winter school sports team that trained at least three days per week.

Each participant performed a vertical jump, long jump, shuttle run, and jump-landing task in a randomized order before and within 10 minutes after completing a standardized warm-up protocol. The groups were matched for participant grade, sex, and sport. All three warm-up programs were limited to 10 to 12 minutes to mimic the time allotted to a normal warm-up.

Research has shown that neuromuscular training reduces injury incidence in children at both the high school and middle school levels.

The static warm-up (SWU) protocol focused on muscle lengthening for the hamstrings, quadriceps, gastrocnemius and soleus complex, hip flexors, and hip adductors. Participants jogged at a comfortable pace for five minutes and then performed five static bilateral stretches. Each stretch was maintained for approximately 30 seconds at a point of mild discomfort.

The dynamic warm-up (DWU) protocol focused on a gradual increase in warm-up intensity, as well as dynamic movements that mimicked actual game play. It was divided into three phases along a 20-m course: dynamic stretching and agility exercises for 10 m, an acceleration run for 10 m, and a recovery jog back to the starting line.

The injury prevention program (IPP) also focused on a gradual increase in warm-up intensity with the same three-phase setup as the DWU. The DWU and IPP included similar exercises, but the IPP also incorporated balance and plyometric exercises.

The groups differed significantly in terms of their improvement from baseline on the jump-landing task; that task was assessed using the Landing Error Scoring System (LESS), which is scored based on errors in landing technique associated with ACL injury risk. The IPP was associated with a greater improvement in LESS scores than the SWU or the DWU. No between-group differences in change scores were observed for the vertical jump, long jump, or shuttle run.

The findings were published in November 2015 by the Journal of Athletic Training.

Although female athletes in general have a higher risk of ACL injury than their male counterparts, the UConn researchers made a point of including youth athletes of both genders.

“We did run pretesting analyses between sexes and did not find any statistical differences, so we opted to combine males and females to evaluate overall warm-up group difference,” Root said. “Also, due to the acute nature of this study, no differences between the two sexes were noted during implementation. While we do agree that girls have an increased risk of ACL injury, males make up a larger overall number of ACL injuries, and we believe that these findings are important for both sexes, particularly at the youth level.”

Although most research on training for ACL injury prevention thus far has involved postpubertal athletes, investigators from Cincinnati Children’s Hospital Medical Center—like their UConn counterparts—have found that neuromuscular training can be effective in youth athletes as well as high schoolers. In a study presented at the 2015 meeting of the National Athletic Trainers Association, researchers randomized 474 female volleyball, basketball, and soccer players to warm-up based neuromuscular training or a sham intervention and found the experimental group had a significantly lower rate of injury over the course of a season.

“Participation in trunk- and hip-focused neuromuscular control exercises reduced injury incidence compared to a sham intervention. This positive protective effect was highly significant at both the high school and middle school level,” said Kim Barber Foss, MS, ATC, an athletic trainer and research biomechanist at the center and lead investigator of the study.